Note 3 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale	$ 159,320,000	$ 171,507,000
Fair Value, Recurring [Member]
Debt Securities, Available-for-sale	159,320,000	171,507,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale	159,320,000	171,507,000
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale	125,678,000	132,678,000
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Recurring [Member]
Debt Securities, Available-for-sale	125,678,000	132,678,000
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale	125,678,000	132,678,000
US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale	33,642,000	38,829,000
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Recurring [Member]
Debt Securities, Available-for-sale	33,642,000	38,829,000
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale	$ 33,642,000	$ 38,829,000